Electrolyte and metabolic derangements

Nikki Jaworski, Ansgar Brambrink

Research output: Chapter in Book/Report/Conference proceedingChapter

1 Scopus citations

Abstract

Acid - base disorders are very common in the NCCU. The normal pH range is 7.35-7.45; alkalosis is defined as pH >7.45, and acidosis is defined as pH <7.35. pH is a measure of the hydrogen ion concentration in the extracellular fluids and is determined by the pCO2 and HCO3 concentration. [H2] (meq/L) = 24 × (PCO2/HCO 3). The initial change in PCO2 or HCO3 is called the primary disorder; the subsequent change is called the compensatory or secondary disorder. Compensatory changes frequently will not return the pH to the normal range but will serve to limit the effect of the primary derangement. Acid - base disorders are of particular concern in neurophysiology because of their effects on cerebral blood flow (CBF). Acidosis (decrease in pH) results in cerebral vasodilation, whereas alkalosis (increase in pH) results in cerebral vasoconstriction. As pH increases, cerebral vasoconstriction also increases, resulting in decreased CBF and therefore decreased cerebral blood volume and ICP. Changes in acid - base status within the blood are transmitted across the blood-brain barrier (BBB) via CO2 rather than by H+ ions; the BBB is impermeable to H+, but CO2 crosses freely. The subsequent change in the CSF pH is a result of the conversion of CO2 + H2O to H+ and HCO3 by carbonic anhydrase. The pH of the CSF returns to normal after 6-8 h, as HCO3 is either retained or extruded across the BBB despite ongoing hyper- or hypocapnia, respectively. As the CSF pH returns to normal, CBF also trends toward normal

Original languageEnglish (US)
Title of host publicationHandbook of Neurocritical Care
Subtitle of host publicationSecond Edition
PublisherSpringer New York
Pages13-35
Number of pages23
ISBN (Print)9781441968418
DOIs
StatePublished - Dec 1 2010

Keywords

  • Acid - base disorders
  • And DI
  • CSW
  • Electrolyte derangement
  • Encephalopathy
  • Endocrinopathies
  • Metabolic disorders
  • SIADH
  • Serum sodium

ASJC Scopus subject areas

  • Medicine(all)

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  • Cite this

    Jaworski, N., & Brambrink, A. (2010). Electrolyte and metabolic derangements. In Handbook of Neurocritical Care: Second Edition (pp. 13-35). Springer New York. https://doi.org/10.1007/978-1-4419-6842-5_2